1. Field of the Invention
The present invention relates generally to a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a device and method for transmitting and receiving data according to a radio link protocol (RLP) used for effective data transmission in radio environments.
2. Description of the Related Art
In general, CDMA mobile communication systems have developed from the IS-95 standard, which mainly provides voice service, into the CDMA-2000 standard, which provides high-speed data service as well as voice service. The CDMA-2000 standard can provide high-quality voice service, moving picture service and Internet search service.
FIG. 1 shows an exemplary packet data service defined by the CDMA-2000 standard. In FIG. 1, a mobile station (MS) includes a terminal equipment (TE) and a mobile terminal (MT). A base station is represented by BS/MSC (Base Station/Mobile Switching Center), and an interworking function block (IWF) connects the BS/MSC to a data network (e.g., Internet). The IWF block is a device for converting protocols from one to another, when different protocols are used. In FIG. 1, the upper layer service (or Web service) processors of the mobile station and the IWF block form messages which are passed down through a network protocol (e.g., Internet protocol (IP)) processor and a link protocol (e.g., point-to-point protocol (PPP)) processor. Then, the data assembled by the upper layer service processors is finally transmitted to the lower layers in the form of a link protocol packet, and the lower layers transmit the data using a proper protocol (e.g., EIA-232, RLP, etc). Although the term “processor” is used herein, it would be understood by one skilled in the relevant art that these are “processes” that may be performed on one or more processors or devices.
FIG. 1 shows an example where an EIA-232 controller is used between the TE and the MT. Generated RLP frames are transmitted over a physical channel connected according to the IS-2000 standard, which is part of the CDMA-2000 standard. The RLP packets received at the base station over the connected physical channel are restored back to link protocol packets and the restored packets are transmitted to the IWF block through the relay layer. In general, interfacing between the base station and the IWF block is performed according to the IS-658 standard. In the IWF block, the link protocol layer reads data from the link protocol packets and transmits the data to the network protocol processor, where the data is finally transmitted to the upper service processor. The distribution of link protocol packets into radio link protocol (RLP) frames through the RLP is one of the subjects of the present invention.
Above, a description has been made of a process for transmitting data from the mobile station to the base station, and it should be noted that the process for transmitting the data from the base station to the mobile station can be performed in a similar manner. To provide various services, the CDMA-2000 standard supports various schemes different from that of FIG. 1. However, they have a common feature in that the link protocol packets with the upper service data are transmitted over the radio physical channel through the RLP.
The present RLP Type-3 specification generates only the RLP frame having a size proper to fill a physical channel frame of 9.6 Kbsp or 19.2 Kbps for the current Rate Set 1, or the RLP frame having a size proper to fill a physical channel frame of 14.4 Kbps or 28.8 Kbps for the Rate Set 2. Therefore, when the physical channel operates at the higher rate of 153.6 Kbps or 230.4 Kbsp, a method is used for filling several RLP frames in one physical channel frame. If the physical channel supports a rate over 153.6 or 230.4 Kbps which is the maximum rate supported in the RLP Type-3 specification, for example, if the physical channel supports the rates of 307.2 Kbps, 460.8 Kbps, 614.4 Kbps and 1036.8 Kbps, more RLP frames can be filled in one physical channel frame. However, as compared with the method for filling one physical channel with one large-sized RLP frame, this method causes an increasing burden on the frame header and unusable parts of the frame, thereby decreasing the frame efficiency. Therefore, to transmit a RLP frame with a size larger than the current RLP Type-3 frame, a new method is required.
One of the important things that should be performed according to the RLP Type-3 specification is to segment a frame into smaller parts (segmented frames) when the size of the frame is greater than the size of the data block allowable for transmission. The conditions of segmentation are as follows:
First, the maximum number of the segmented frames is 3, i.e., first, second and last segmented frames. If the frame needs to be segmented into more than the three parts, it is not transmitted until it can be segmented into three parts.
Second, the reassembling of the segmented frames is only allowed when all of the segmented frames have been received Thus, if one of three segmented frames (first, second or last) is not received, all of the three segmented frames are retransmitted.
However, the RLP type-3 specification can only generate the RLP frame with a size adequate for filling the physical channel frame of 9.6 Kbsp or 19.2 Kbps for the Rate Set 1 or the RLP frame with a size adequate for filling the physical channel frame of 14.4 Kbps or 28.8 Kbps for the Rate Set 2. This means that, at maximum, three segmented frames must suffice for transmission, which is acceptable at the lowest transmission rates of 9.6 Kbps or 14.4 Kbps. However, if the physical channel has a greater transmission rate, which uses a greater RLP frame in order to improve the transmission efficiency of the RLP, another segmentation method is required different from the conventional segmentation.